Dust, pollen, smoke, smog, bacteria, virus, mold and odors are all comprised of particles which can be suspended in the air. These airborne particles are small, ranging in size from 0.001 microns to 10 microns. Larger particles of 10 to 50 microns tend to settle out quickly while smaller particles, the main hazard to health, remain airborne.
These suspended particles can be removed from the air by either mechanical or electrical means. The most common mechanical techniques include fan/filter systems, gravity settling, centrifugal separation, and scrubbing.
In ordinary fan/filter systems air is drawn through a filter which mechanically traps particles in a web of synthetic or glass fibers. The efficiency of these filters is dependent on the filter surface area and the density of the web network. At low air resistance densities, these filters are only effective for large particles exceeding 10 microns. Fan/filter systems may also involve activated carbon and/or silica gel materials to remove odors. The efficiency and effectiveness of these approaches are grossly limited, so that scents or perfumes are often used to make the filtered air smell “clean”.
For small particle removal, a high efficiency, particle air (HEPA) filter having accordion-like pleats is used. These are expensive and used for special applications where a single pass efficiency is required, such as in hospitals and clean rooms, and they must be changed frequently before they become clogged and overburden the air circulation fan.
Electrical particle removal may be achieved by either electrostatic precipitation or open-air ion generation. Electronic deposition of particles is accomplished by charging the particles to be deposited with one polarity and grounding the objects on which the particles are to be deposited with the opposite polarity or common line ground.
The accepted theory of operation of a conventional electrostatic precipitation system involves air being drawn by a fan past an electrode that gives the airborne particles a relatively strong electric charge. The air then passes by a set of parallel collector plates of opposite charge to which the particles are attracted and stick. Essentially, electrostatic precipitation uses electrical forces of charged bodies to separate particles from the air where the polarization forces are perpendicular to the direction of the air flow. This process is highly effective on small airborne pollutants ranging in size from 0.001 to 10 microns (0.0000003 to 0.0004 inches).
A further issue involves the presence of free air ions. The air in typical indoor spaces is almost totally devoid of free air ions because any existing ions become attached to dust particles which then become attracted to and attached to nearby wall and floor surfaces. Thus the indoor air is essentially scrubbed free of nearly all free air ions, and there are no natural sources indoors to replace them. Outdoors, there are numerous sources of free air ions such as the effects of sunlight, waterfalls, ocean waves, and even pine forests.
Air ions function outdoors to naturally remove bacteria and small particles from the air, and their absence in indoor air can lead to easier spreading of infectious diseases. Air ions are also thought to affect moods, with an over-abundance of positive ions causing depression, and with a balanced level of free air ions being optimum for well-being.
U.S. Pat. No. 4,978,372 to Pick discloses a pleated charged media air filter for an electrostatic air filtration system of the charged media type wherein contact between the filter media and the electrostatic charging media of the filter is minimized or eliminated to increase the efficiency of the filter. The fibrous filter media is either corrugated to minimize its contact with the charging media or separated from the charging media by nonconductive spacers. This dramatically increases the efficiency of the filter by reducing the voltage drop on the charged media caused by conduction across a filter medium in close contact with both a charged and a grounded medium.
U.S. Pat. No. 5,474,600 to Volodina, et al. describes an apparatus for biological purification and filtration of air. The apparatus includes a coarse filter, an ionizer, an additional plate and a fine filter, which are installed in this order along the path of the gas flow, and a power source. The coarse filter is essentially an electrostatic precipitator consisting of three plates adjacent to each other, the outer-most of which are made of a cellular metal and are connected electrically to the opposite-in-sign terminals of the power source, whereas the central plate is made of polyurethane foam. The coarse filter abuts closely on the cylindrical nondischarge electrode of the ionizer.
U.S. Pat. No. 5,593,476 to Coppom teaches a method and apparatus for use in electronically enhanced air filtration. A high efficiency air filtration method and apparatus utilizes a fibrous filter medium that is polarized by a high potential difference which exists between two electrodes. The electrodes include an insulated electrode and an uninsulated electrode. A corona precharger is positioned upstream of the electrodes and filter. The corona precharger creates charged particles that have an opposite charge (e.g., a positive of negative charge) determined with respect to a polarization dipole proximal to the insulated electrode. These particles cancel a trapped charge that tends to accumulate on the filter surfaces proximal to the insulated electrode.
U.S. Pat. No. 5,855,653 to Yamamoto teaches an induced voltage electrode filter system with a disposable cartridge. A filter apparatus for trapping particles suspended in gaseous fluid stream generally includes a first and a second electrode with a porous filter therebetween along with electrical contacts for applying a DC voltage across the first and second electrodes. A third electrode is provided and a frame is included for removably supporting a porous filter, along with the first, second, and third electrodes in order to electrify, by induction, the third electrode with a voltage in the third electrode in order to increase trapping of the particles by the filter apparatus.
The foregoing patents reflect the current state of the art of which the present inventor is aware. Reference to, and discussion of, these patents is intended to aid in discharging Applicant's acknowledged duty of candor in disclosing information that may be relevant to the examination of claims to the present invention. However, it is respectfully submitted that none of the above-indicated patents disclose, teach, suggest, show, or otherwise render obvious, either singly or when considered in combination, the invention described and claimed herein.